This invention relates generally to methods of evaluating fibrous synthetic polymers. More specifically, the invention relates to a method for quantifying nodal characteristics in fluid entangled filaments.
In the synthetic fiber industry, it has long been recognized that yarn bundles should be coherent for processing at high rates of speed. Initially, such yarns were made by twisting. But twisted yarn is expensive and complicated to produce.
Responding to the need for inexpensive coherent yarn filaments, fiber manufacturers discovered that yarns could be interlaced. Later it was recognized that interlacing was a means to mix fibers of different types, such as color or dye affinity. U.S. Pat. No. 3,846,968 to Sheehan et al. demonstrates a mixed fiber application of interlacing.
An interlaced yarn is characterized by points of entanglement, called nodes, which are separated by spaces of unentangled filaments. Commonly, individual yarn filaments are interlaced by exposing the filament bundle to a localized fluid jet. U.S. Pat. No. 2,985,995 and 3,110,151, both to Bunting, Jr., et al. describe several methods of inducing interlacing by fluid impingement. These patents show what is referred to herein as a hard tight node (see U.S. Pat. No. 2,985,995, FIG. 25). One such interlacer has openings at various angles of a rotary wheel design. The rotary wheel turns with the yarn and creates an even spacing which can result in patterning of yarns having different color components in the final product. For the purposes of the present invention, "even" spacing means essentially equal distance between nodes. The Bunting, Jr., et al. patents teach that more than one interlacer can be used in series and that the spacing of nodes can be varied between random and periodic by adjusting the fluid temperature, processing speed and finish. To accomplish these objectives, the Bunting, Jr., et al. interlacers are designed for free movement of the filaments in the yarn passage.
Many methods for interlacing filaments refer to the node spacing as random or irregular. However, for certain applications of yarns made from two or more contrasting filaments with, for example, different dye affinities or which are precolored differently, for example heather carpets, as presented in U.S. Pat. Nos. 4,223,520 to Whitted et al., 4,570,312 to Whitener, Jr., and 4,697,317 to Nelson, it is important that the nodes be regularly spaced. Otherwise, the nodeless gaps show up in the carpet as stria or short sections. A series of stria can appear as a streak, like the dashes in the road form a center line. As used herein, "regular" nodes are nodes with unequal spacing having no gaps between them above 6 cms.
There are methods of periodically interlacing filaments. As used herein, a periodically interlaced filament is one having internodal spacing which is even or regular. For example, U.S. Pat. No. 3,115,691 to Bunting, Jr., et al. describes a single interlacing apparatus having two jet streams therein. According to the patent, the arrangement results in a greater degree of entanglement.
U.S. Pat. No. 3,426,406 to McCutchan, Jr. describes an interlacing apparatus designed to overcome randomness and streaking. At least one pair of opposed fluid conduits having a common longitudinal axis which intercepts and is perpendicular to the axis of an elliptical yarn passageway achieves the objective.
U.S. Pat. No. 3,474,510 to Torsellini describes a method to overcome randomness in the prior devices by exposing the yarn moving under tension to fluid pulses. The pulses occur at constant time intervals and act on the yarn from different directions.
U.S. Pat. No. 3,563,021 to Gray describes the use of cooperating tandem jets to achieve a uniformly interlaced yarn. The oscillation of the filament bundle produced by the first jet acts to traverse the yarn between the orifices of the other jet.
U.S. Pat. Nos. 4,064,686 and 4,223,520, both to Whitted et al., are directed to an interlaced yarn having alternatingly twisted nodes. That is, one node is twisted counterclockwise, the next is twisted clockwise and so on. This is achieved by using diametrically opposed fluid passages in the entangling apparatus. The stretching in the interlacing apparatus can be changed by adjusting the tension so that some portions are stretched more than others and, upon dyeing, cause a color differential.
In addition, there are several methods for producing novelty yarns by various entangling procedures. One such yarn is disclosed in U.S Pat. No. 3,846,968 to Sheehan et al. The yarn has a particular structure from being entangled in the entangling apparatus.
U.S. Pat. No. 4,152,885 to Cox, Jr., describes an interlocked yarn wherein at least one of the individual filaments in the bundle encircles the other filaments to interlock the filaments together. The yarn is made by feeding the filament bundle into a fluid medium flowing opposite of the direction of bundle travel.
U.S. Pat. No. 4,152,886 to Nelson describes a yarn which is intermittently debulked by passing a stream of heated gas through the yarn while it is under tension. The process achieves varying levels of bulking and debulking.
U.S. Pat. No. 4,697,317 to Nelson is directed to a randomly-spaced, tightly entangled nub yarn and the process and apparatus for making the same. As a starting point, the process uses crimped and interlaced supply yarn. Nelson uses the term "nub" to denote what is referred to herein as a hard node. According to this Nelson patent, the nubs can be up to 1 inch (2.54 cm) long.
Although the above patents often result in filaments with node spacing such as the even node spacing produced by the rotary wheel interlacer of U.S. Pat. No. 3,110,151, such node spacing is not an answer to the problem of stria caused by nodeless gaps. As an illustration, exactly even node spacing can result in patterning in some carpet constructions which resembles that experienced from the twist cabled ends of multicolored bulked continuous filament (BCF).
A further problem encountered in producing interlaced yarn which is suitable for applications requiring uniformity, such as carpet applications, is that air entangling conditions which are severe enough to insure regular nodes also produce excessively tight nodes. These hard nodes, like the "nubs" of Nelson, reduce carpet yarn cover in carpet applications, give the carpet a harsh hand and also make tufting difficult. Thus soft node yarn is desirable for both mixed fiber and unmixed (homogeneous) fiber yarns. For homogeneous yarns, soft nodes maintain consistent coherence without sacrificing cover with hard knots, or affecting the carpet tufting by nubbiness in the face or picks from hard nodes in the tufting needles.
Previously known means to soften the nodes result in undesirable effects. For example, reduction of fluid flow rate or increased process speed causes unacceptably irregular spacing between nodes which can, as noted, cause streaking due to stria. On the other hand, at a given fluid flow rate, slowing down the process speed makes the nodes harder and also limits production rate. Reducing the yarn tension can cause a high degree of yarn fuzziness which then interferes with further handling like tufting. Also, low tensions make consistency difficult to maintain and the process difficult to control.
In the development of interlaced yarns having desirable properties discussed above for intended end uses, it has been problematic to quantify the entanglement characteristics. Thus, there remains a need for methods to so characterize the yarns.